The invention relates to chip resistant pneumatic tires, especially off-the-road (OTR) tires and heavy duty off-the-road tires having typically 1 to 36 carcass plies and 6 belts (in a radial ply tire) or 4 breakers (in a bias ply tire), and one to four sets of beads.
Heavy-duty off-the-road tires, because of the nature of their use, are exposed to chipping and chunking caused by sharp rocks and uneven terrain. A number of means have been used in the prior art to confront this problem with varying degrees of success.
U.S. Pat. No. 5,173,136 issued Dec. 22, 1992, teaches incorporating RFL coated monofilament fibers into the tread rubber and sidewall rubber of mining tires.
U.S. Pat. No. 5,490,550 teaches the use of continuous wire filaments incorporated as a barrier in the tread and/or sidewall of off-the-road tires.
Experience has shown that a well-constructed steel reinforced OTR tire is more durable than those made with organic reinforcement.
A high sulfur rubber is used to coat steel reinforcement to improve adhesion between rubber and steel. Although generally cut resistant and durable, the inventors have observed more chipping and chunking in the tread of steel reinforced tires than is seen in less rigid tires. In the conception of the invention, the inventors theorized that if a rubber having high compatibility with tread rubber is used as a barrier between the tread and steel reinforcement, such compatibility might better distribute forces on the tread to a larger portion of the tire, and help prevent chipping and chunking. Additional reinforcement in the rubber may further enhance such a force distribution.
Low sulfur rubber is used in reinforced plies incorporating nylon reinforcement, and such rubber tends to be more resilient.
Organic monofilament reinforcement has been used in the past as a barrier ply in truck tires as shown in U.S. Pat. No. 5,743,975, which teaches the use of nylon monofilament top belts in radial medium truck tires. Such monofilament reinforcement has been used to minimize cutting of the tread and increase retreadability in RMT tires.
It is an object of the present invention to provide a chip resistant tire.
Other objects of the invention will be apparent from the following specification and claims.
U.S. Pat. No. 1,201,257 to Cobb relates to a fabric for tires in which longitudinal wire cords or filaments are interwoven with organic fibers. The structure described is used in a crown area of the tire as a belt structure.
U.S. Pat. No. 1,207,709 to Campbell relates to fabric for tires in which wire is interwoven with organic cords or fibers in a wire/organic composite structure.
U.S. Pat. No. 1,228,650 to Christian relates to a pneumatic tire in which a woven wire fabric is used in the crown area and upper sidewall of the tire. The woven wire structure is said to provide resistance against perforation, lines 17-18, and blowouts resulting from high internal pneumatic pressure, and from injury termed xe2x80x9cstone bruisexe2x80x9d, lines 27-30.
U.S. Pat. No. 2,987,095 to Toulmin, Jr. relates to a tire cord structure and describes a tire wherein reinforcing metal is incorporated and thoroughly united with the rubber in the body of the casing. The individual strands may be woven to provide a fabric structure or interwoven middle layer, column 2, lines 43-45.
U.S. Pat. No. 4,235,274 to Suzuki et al, relates to a tire structure having a reinforcing layer composed of a helically formed filament or bundle of wire in the crown area of the tire. According to the claims, the bundle comprises at least two filaments and in use in a tire, it appears that five to seven filaments comprise the bundle used.
A chip resistant pneumatic tire 10 is provided which comprises at least a pair of parallel annular beads 12, carcass plies 14 comprising parallel cord reinforcement wrapped around the beads, a tread 18 disposed over the carcass plies 14 in a crown area of the tire 10, belt or breaker reinforcement 16 interposed between the tread 18 and carcass 14, and sidewalls 20 disposed over the carcass plies 14 between the tread 18 and the beads 12. The tires 10 may be bias ply or radial ply construction.
The improvement in the tire comprises the inclusion of plies comprising continuous organic reinforcement in a rubber reinforced rubber sheet 22,22b in or under the tread and/or sidewall. The reinforcement may be monofilaments or cords 11. Two organic monofilaments 11 may be used together.
The cords or filaments used in the reinforced rubber sheet 22,22b are at least 2000 denier (2200 dTex) and have a tenacity of at least 3.5 g/denier (31 cN/Tex), an initial modulus of at least 20 g/denier (177 cN/Tex), an elongation at break of at least 10% and a shrinkage of at most 10%.
In an illustrated embodiment, reinforced rubber sheet 22, wherein the reinforcement therein makes an angle of 50xc2x0 to 70xc2x0 with respect to the EP of the tire, is placed over the belt package 16 of a tire 10.
In the illustrated embodiment, 9000 denier (10,000 dTex) round monofilaments having a tenacity of 37 cN/Tex and an initial modulus (greige) of 194 cN/tex were used as reinforcement in an reinforced rubber sheet 22 used to build a tire 10 of the invention.
In a specific illustrated embodiment of the invention, the reinforced rubber sheet 22 is a nylon monofilament reinforced ply wherein the reinforcement cords 11 have an angle of 60xc2x0 with respect to the equatorial plane (EP) of the tire. In such constructions, an organic monofilament reinforced ply is used as an overlay/top breaker wherein the ply does or does not extend beyond the edges of the other breakers, and the angles of the reinforcing cords are maintained in substantially the same direction as the steel reinforcement cords in the breaker ply next radially below, or are at directions which cross said steel reinforcement cords.
As used herein and in the claims, the terms
xe2x80x9cAxialxe2x80x9d and xe2x80x9caxiallyxe2x80x9d refer to directions which are parallel to the axis of rotation of a tire,
xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d refer to directions that are perpendicular to the axis of rotation of a tire,
xe2x80x9cBeadxe2x80x9d refers to that part of a tire comprising an annular tensile member wrapped by ply cords and shaped, with or without other reinforcement elements to fit a designed tire rim,
xe2x80x9cCarcassxe2x80x9d refers to the tire structure apart from the belt structure, tread, undertread, and sidewall rubber but including the beads, (carcass plies are wrapped around the beads),
xe2x80x9cBeltxe2x80x9d or xe2x80x9cbelt plyxe2x80x9d refers to an annular layer or ply of parallel cords, woven or unwoven, underlying the tread, not anchored to the bead, and having cord angles of from 12xc2x0 to 35xc2x0 with respect to the EP of the tire,
xe2x80x9cBreaker pliesxe2x80x9d refers to annular reinforcement members in the crown area of a bias ply tire having longitudinal reinforcement members having an angle (in the illustrated embodiment) with respect to the equatorial plane of the tire,
xe2x80x9cCrownxe2x80x9d refers to substantially the outer circumference of a tire where the tread is disposed,
xe2x80x9cLasexe2x80x9d refers to load at specified elongation.
xe2x80x9cEquatorial plane (EP)xe2x80x9d refers to a plane that is perpendicular to the axis of rotation of a tire and passes through the center of the tire""s tread,
xe2x80x9cObroundxe2x80x9d refers to a cross sectional shape having a width greater than its height and having no sharp corners (e.g. oval), and generically is intended to include similar rounded shapes,
xe2x80x9cRivetxe2x80x9d refers to the amount of space between two adjacent cords,
xe2x80x9cTenacityxe2x80x9d refers to breaking stress expressed as force per unit linear density of an unstrained specimen (cN/Tex or gm/denier), (usually used in textiles),
xe2x80x9cModulusxe2x80x9d refers to the ratio of the change in stress to the change in strain, and
xe2x80x9cOrganicxe2x80x9d refers to compounds, including polymers, containing a carbon backbone or structure, which can be shaped, stretched of formed into a particular physical configuration.